Electrical vacuum-discharge tube



S. RUBEN ELECTRICAL VACUUM mscH'ARes TUBE Filed Jan.l7, 1924 Patented Nov. 15, 1927. 1

.SAMIIELQRUBEN, or .NEW YORK, N. .Y.

EIIECTRICAL VACUUM-"DISCHARGE TUBE.

Application file'dlanuary 17, 1924. Serial'No.'686,852.

i This invention relates to an electrical'vac- 'uum discharge tube and more particularly,

it relatcs toan ray tube in which c'onducti'on through the vacuous space is effected i tln-oughcontrol of the vaporpressure Of an alkaline 'metal contained 'therewithin. Its chief object to provide :an efficient ray tube normally having constant discharge characteristics and-externally-controllable by varying *the vapor pressure of an alkaline metal within the tube.

In the prior art there are two commonly used types f ray tubes. one depending upon the electron conduction between its cathode and anode elements, the other :de-

pending upon ionic discharge conduction therc between by means of a gas or vapor supply.- Inthe latter or ionic-type, an electrical discharge between its cathode and anode 'is :e'i'fected through the medium of a residual gas or vapor within the tube, and, 'on its absorption by the tube elements, is

replenished through a gas or vapor liberated tor vapor adwstmentfrom a material combined with carbon dioxide or water vapor, by the application of heat. The adjustment iscontinued until *the desired pressure condition for the electrical discharge is reest-ab lished. 'Thistype is' very unstable inoperation and requires continualadjustment-ofits gas content, as its operation is dependent upon ionic "bombardmentof its cathodeto ctFect -a 'discl'iarge of electrons to the anode. It requires a direct current from a high potential source. v

Broadly, 'th's invention consists of a'vacnum -tu'be evacuated toya pressure at which negligil'ile positiveionization can occur, and containing an alkaline meta'l which, when heated, produces 'an increased vapor pressure which permits a current conduction between V the electrodes, =upon 'the application thereto of' suliicient potential. 1

"The invention comprises anionic conduct- ,ing tu'befhaving normally constant pressure charactoristics,the operation "tactorof which is variable to a degree not possessed by the ionic discharge tubes of the prior art. It

consists of a highly evacuated tu'bc having,

in a chamber-connecting with that containing the cathode and anode elements, an alkaline metal, such, for instance,'as sodium, the va poi pressure of which at normal operating temperatures, is insufficient :tor practicable ionic conduction between the electrodes, but

which is controllable by the application of duction being thus controllable at fixed -po tentials. At ordinary or room temperatures,

the application of high potentials to the electrodes effects negligible ionic conduction 7 heat :to the *metal, the degree 'of-ionic con- :betweenthenr; but, upon the "application-Off heat to the alkaline metal an increase in its vapor pressure occurs, permittmg sufficient electrical conduction between the electrodes.

The electron discharge in part .is due to the photoelectric character of the alkaline metal 'vapor under the influence of short wave radiations from the anode andfrom secondary ionization of the vapor.

Any residual vgas emitted from the tube elements is both chemically and-physically absorbed by the alkaline metal vapor, which maintainsa constantinitial discharge characteristic forthe tube. Inthis tiibe geometrical factors can be-employed in the d'esign o'f the cathode and anode elements, which permits self-rectification. Preferably the cathode is composed of a material having a veryihigh thermal conductivity and melting point and is pointed at the discharge end. I have toundhardened copperto-make a very satisfactory cathode. The: anode is of the type commonly used in tubes of this kind, that is, composed ofa refractory material, such as tungsten.-employedasithe target, in close contactwith a metal of high heat conductivity, such asc'op'per. Oscillographic :record-s of the operation of the tube "indicate characteristics different fromthose of tubes o'f'the prior art; the current 'flows between the electrodesonl-y at the maximum values of the applied alternating "current oscillations. which efi'ects an increased efficiency in X production, comparedwith that of the tubes of the prior'art, all of which'use the low amplitude values of the applied oscillations, which produce undes'ira'ble radiations of longer wave lengths;

The principle employed oan best be explained in connection with a certain "illustrative embodiment o'f the invention shown in the accompanying drawings, in which,

; Fig. 1 shows an X ray tube of this inventarget 2,, for, the electron bombardment, the anode being held in place by the metal ferrule 4:, and having its lead at 8. At 5 is rep resented the chamber containing alkaline metal. The lead from the cathode is shown at 7 and at 6 is a metal plug for holding the tube in a socket. The various other elements in the electrical circuit are the alternating current generator 12, transformers 9 and 10, with their respective primaries and secondaries P and S, and. P, and S and variable resistance 11.

Referring more particularly to Fig. 2, 15 represents the heating wire wound about chamber 5, containing alkaline metal 16, heat insulated by a lay-er of asbestos 14, and an electrical insulating shell 13.

The operation of the tube is as follows: Alternating current of high potential as generated at 12, is applied to electrodes 1 and 2, through transformer 9. At normal temperatures there is negligible discharge between the electrodes due to positive ioniza- .tion, until heat is applied by transformer 10, and controlled by. resistance 11, to the alkaline metal 16, when its vapor pressure is increased and through the ionic bombardment of the cathode, a stream of electrons dis charges from the cathode to the target 2,, from which the X rays are radiated.

The tube walls and the anode and connecting parts become highlyjheated by thermal radiation from the anode during the operation of the tube, resulting in the discharge of alkaline metal vapor from the walls. The cathode chamber, though somewhat heated to obtain the increase of the vapor pressure of the alkaline metal, is the coolest part of the tube after being in operation.

The cathode, being pointed at its discharge end, allows more current to flow in one direction, due to which self rectification results.

What I claim is:

1. An X ray tube comprising a sealed envelop, exhausted to a pressure at which at normal temperature no positive ionization can occur, and containing a cathode and an anode, said cathode composed of metal of high thermal conductivity, and a mass of alkaline metal, in combination with means for establishing a potential between said cathode and anode, and means for applying heat independently to said alkaline metal.

2. An X ray tube comprising a sealed envelop, exhausted to a pressure at which at normal temperature substantially no positive ionization can occur, and containing a cathode and an anode and a mass of alkaline metal, said cathode composed of metal of high thermal conductivity and pointed on the part thereof facing said anode, in combination with means for establishing a potential between said cathode and anode, and means for applying heat independently to said alkaline metal to raise the vapor pressure of the tube and increase the ionic conduction between the electrodes.

3. An X ray tube comprising a sealed envelop evacuated to a pressure at which, at the normal vapor pressure therein, substantially no positive ionization can occur, and containing cooperating electrodes and a mass of alkaline metal, and means for maintaining an ionic discharge between the electrodes at a potential, insuflicient at normal vapor pressure in the tube to maintain an ionic discharge, comprising means independent of said discharge for heating the alkaline metal.

l. An X ray tube comprising a gas-tight vessel evacuated to a pressure at which substantially no positive ionization can occur, and containing cooperating electrodes and a mass of alkaline metal and means for establishing a potential between said electrodes and means for maintaining an electrical discharge between said electrodes, at a given potential by controlling'the vapor pressure within said tube by heating said alkaline metal by a source independent of said discharge.

5. An X ray tube comprising a gas-tight vessel evacuated to a pressure at which substantially no positive ionization can occur, and containing cooperating electrodes and a mass of sodium, and means for establishing a potential between said electrodes, and means for maintaining an electrical discharge between said electrodes at a given po tential by controlling the vapor pressure within said tube by heating said sodium by a source independent of said discharge.

6. An X ray tube comprising a sealed envelop, exhausted to a pressure at which at normal temperatures,;no positive ionization can occur, and containing a'cathode and an anode, said cathode being composed ofa metal of high thermal conductivity, and a mass of alkaline metal, in combination with means for establishing a potential between said electrodes, and means for raising the vapor pressure within the tube byapplying heat to said alkaline metal, independent of a discharge between the electrodes.

Signed at New York, .in the county of New York and State of New York, this 12th day of January A. D. 1924-.

SAMUEL RUBEN. 

